1 ------------------------------------------------------------------------------
2 T H E /proc F I L E S Y S T E M
3 ------------------------------------------------------------------------------
4 /proc/sys Terrehon Bowden <terrehon@pacbell.net> October 7 1999
5 Bodo Bauer <bb@ricochet.net>
7 2.4.x update Jorge Nerin <comandante@zaralinux.com> November 14 2000
8 move /proc/sys Shen Feng <shen@cn.fujitsu.com> April 1 2009
9 ------------------------------------------------------------------------------
10 Version 1.3 Kernel version 2.2.12
11 Kernel version 2.4.0-test11-pre4
12 ------------------------------------------------------------------------------
13 fixes/update part 1.1 Stefani Seibold <stefani@seibold.net> June 9 2009
19 0.1 Introduction/Credits
22 1 Collecting System Information
23 1.1 Process-Specific Subdirectories
25 1.3 IDE devices in /proc/ide
26 1.4 Networking info in /proc/net
28 1.6 Parallel port info in /proc/parport
29 1.7 TTY info in /proc/tty
30 1.8 Miscellaneous kernel statistics in /proc/stat
31 1.9 Ext4 file system parameters
33 2 Modifying System Parameters
35 3 Per-Process Parameters
36 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer
38 3.2 /proc/<pid>/oom_score - Display current oom-killer score
39 3.3 /proc/<pid>/io - Display the IO accounting fields
40 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
41 3.5 /proc/<pid>/mountinfo - Information about mounts
42 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
43 3.7 /proc/<pid>/task/<tid>/children - Information about task children
44 3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file
45 3.9 /proc/<pid>/map_files - Information about memory mapped files
46 3.10 /proc/<pid>/timerslack_ns - Task timerslack value
47 3.11 /proc/<pid>/patch_state - Livepatch patch operation state
52 ------------------------------------------------------------------------------
54 ------------------------------------------------------------------------------
56 0.1 Introduction/Credits
57 ------------------------
59 This documentation is part of a soon (or so we hope) to be released book on
60 the SuSE Linux distribution. As there is no complete documentation for the
61 /proc file system and we've used many freely available sources to write these
62 chapters, it seems only fair to give the work back to the Linux community.
63 This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm
64 afraid it's still far from complete, but we hope it will be useful. As far as
65 we know, it is the first 'all-in-one' document about the /proc file system. It
66 is focused on the Intel x86 hardware, so if you are looking for PPC, ARM,
67 SPARC, AXP, etc., features, you probably won't find what you are looking for.
68 It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
69 additions and patches are welcome and will be added to this document if you
72 We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
73 other people for help compiling this documentation. We'd also like to extend a
74 special thank you to Andi Kleen for documentation, which we relied on heavily
75 to create this document, as well as the additional information he provided.
76 Thanks to everybody else who contributed source or docs to the Linux kernel
77 and helped create a great piece of software... :)
79 If you have any comments, corrections or additions, please don't hesitate to
80 contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this
83 The latest version of this document is available online at
84 http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html
86 If the above direction does not works for you, you could try the kernel
87 mailing list at linux-kernel@vger.kernel.org and/or try to reach me at
88 comandante@zaralinux.com.
93 We don't guarantee the correctness of this document, and if you come to us
94 complaining about how you screwed up your system because of incorrect
95 documentation, we won't feel responsible...
97 ------------------------------------------------------------------------------
98 CHAPTER 1: COLLECTING SYSTEM INFORMATION
99 ------------------------------------------------------------------------------
101 ------------------------------------------------------------------------------
103 ------------------------------------------------------------------------------
104 * Investigating the properties of the pseudo file system /proc and its
105 ability to provide information on the running Linux system
106 * Examining /proc's structure
107 * Uncovering various information about the kernel and the processes running
109 ------------------------------------------------------------------------------
112 The proc file system acts as an interface to internal data structures in the
113 kernel. It can be used to obtain information about the system and to change
114 certain kernel parameters at runtime (sysctl).
116 First, we'll take a look at the read-only parts of /proc. In Chapter 2, we
117 show you how you can use /proc/sys to change settings.
119 1.1 Process-Specific Subdirectories
120 -----------------------------------
122 The directory /proc contains (among other things) one subdirectory for each
123 process running on the system, which is named after the process ID (PID).
125 The link self points to the process reading the file system. Each process
126 subdirectory has the entries listed in Table 1-1.
129 Table 1-1: Process specific entries in /proc
130 ..............................................................................
132 clear_refs Clears page referenced bits shown in smaps output
133 cmdline Command line arguments
134 cpu Current and last cpu in which it was executed (2.4)(smp)
135 cwd Link to the current working directory
136 environ Values of environment variables
137 exe Link to the executable of this process
138 fd Directory, which contains all file descriptors
139 maps Memory maps to executables and library files (2.4)
140 mem Memory held by this process
141 root Link to the root directory of this process
143 statm Process memory status information
144 status Process status in human readable form
145 wchan Present with CONFIG_KALLSYMS=y: it shows the kernel function
146 symbol the task is blocked in - or "0" if not blocked.
148 stack Report full stack trace, enable via CONFIG_STACKTRACE
149 smaps an extension based on maps, showing the memory consumption of
150 each mapping and flags associated with it
151 numa_maps an extension based on maps, showing the memory locality and
152 binding policy as well as mem usage (in pages) of each mapping.
153 ..............................................................................
155 For example, to get the status information of a process, all you have to do is
156 read the file /proc/PID/status:
158 >cat /proc/self/status
186 SigPnd: 0000000000000000
187 ShdPnd: 0000000000000000
188 SigBlk: 0000000000000000
189 SigIgn: 0000000000000000
190 SigCgt: 0000000000000000
191 CapInh: 00000000fffffeff
192 CapPrm: 0000000000000000
193 CapEff: 0000000000000000
194 CapBnd: ffffffffffffffff
197 voluntary_ctxt_switches: 0
198 nonvoluntary_ctxt_switches: 1
200 This shows you nearly the same information you would get if you viewed it with
201 the ps command. In fact, ps uses the proc file system to obtain its
202 information. But you get a more detailed view of the process by reading the
203 file /proc/PID/status. It fields are described in table 1-2.
205 The statm file contains more detailed information about the process
206 memory usage. Its seven fields are explained in Table 1-3. The stat file
207 contains details information about the process itself. Its fields are
208 explained in Table 1-4.
210 (for SMP CONFIG users)
211 For making accounting scalable, RSS related information are handled in an
212 asynchronous manner and the value may not be very precise. To see a precise
213 snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
214 It's slow but very precise.
216 Table 1-2: Contents of the status files (as of 4.8)
217 ..............................................................................
219 Name filename of the executable
220 Umask file mode creation mask
221 State state (R is running, S is sleeping, D is sleeping
222 in an uninterruptible wait, Z is zombie,
223 T is traced or stopped)
225 Ngid NUMA group ID (0 if none)
227 PPid process id of the parent process
228 TracerPid PID of process tracing this process (0 if not)
229 Uid Real, effective, saved set, and file system UIDs
230 Gid Real, effective, saved set, and file system GIDs
231 FDSize number of file descriptor slots currently allocated
232 Groups supplementary group list
233 NStgid descendant namespace thread group ID hierarchy
234 NSpid descendant namespace process ID hierarchy
235 NSpgid descendant namespace process group ID hierarchy
236 NSsid descendant namespace session ID hierarchy
237 VmPeak peak virtual memory size
238 VmSize total program size
239 VmLck locked memory size
240 VmPin pinned memory size
241 VmHWM peak resident set size ("high water mark")
242 VmRSS size of memory portions. It contains the three
243 following parts (VmRSS = RssAnon + RssFile + RssShmem)
244 RssAnon size of resident anonymous memory
245 RssFile size of resident file mappings
246 RssShmem size of resident shmem memory (includes SysV shm,
247 mapping of tmpfs and shared anonymous mappings)
248 VmData size of private data segments
249 VmStk size of stack segments
250 VmExe size of text segment
251 VmLib size of shared library code
252 VmPTE size of page table entries
253 VmSwap amount of swap used by anonymous private data
254 (shmem swap usage is not included)
255 HugetlbPages size of hugetlb memory portions
256 Threads number of threads
257 SigQ number of signals queued/max. number for queue
258 SigPnd bitmap of pending signals for the thread
259 ShdPnd bitmap of shared pending signals for the process
260 SigBlk bitmap of blocked signals
261 SigIgn bitmap of ignored signals
262 SigCgt bitmap of caught signals
263 CapInh bitmap of inheritable capabilities
264 CapPrm bitmap of permitted capabilities
265 CapEff bitmap of effective capabilities
266 CapBnd bitmap of capabilities bounding set
267 NoNewPrivs no_new_privs, like prctl(PR_GET_NO_NEW_PRIV, ...)
268 Seccomp seccomp mode, like prctl(PR_GET_SECCOMP, ...)
269 Cpus_allowed mask of CPUs on which this process may run
270 Cpus_allowed_list Same as previous, but in "list format"
271 Mems_allowed mask of memory nodes allowed to this process
272 Mems_allowed_list Same as previous, but in "list format"
273 voluntary_ctxt_switches number of voluntary context switches
274 nonvoluntary_ctxt_switches number of non voluntary context switches
275 ..............................................................................
277 Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
278 ..............................................................................
280 size total program size (pages) (same as VmSize in status)
281 resident size of memory portions (pages) (same as VmRSS in status)
282 shared number of pages that are shared (i.e. backed by a file, same
283 as RssFile+RssShmem in status)
284 trs number of pages that are 'code' (not including libs; broken,
285 includes data segment)
286 lrs number of pages of library (always 0 on 2.6)
287 drs number of pages of data/stack (including libs; broken,
288 includes library text)
289 dt number of dirty pages (always 0 on 2.6)
290 ..............................................................................
293 Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
294 ..............................................................................
297 tcomm filename of the executable
298 state state (R is running, S is sleeping, D is sleeping in an
299 uninterruptible wait, Z is zombie, T is traced or stopped)
300 ppid process id of the parent process
301 pgrp pgrp of the process
303 tty_nr tty the process uses
304 tty_pgrp pgrp of the tty
306 min_flt number of minor faults
307 cmin_flt number of minor faults with child's
308 maj_flt number of major faults
309 cmaj_flt number of major faults with child's
310 utime user mode jiffies
311 stime kernel mode jiffies
312 cutime user mode jiffies with child's
313 cstime kernel mode jiffies with child's
314 priority priority level
316 num_threads number of threads
317 it_real_value (obsolete, always 0)
318 start_time time the process started after system boot
319 vsize virtual memory size
320 rss resident set memory size
321 rsslim current limit in bytes on the rss
322 start_code address above which program text can run
323 end_code address below which program text can run
324 start_stack address of the start of the main process stack
325 esp current value of ESP
326 eip current value of EIP
327 pending bitmap of pending signals
328 blocked bitmap of blocked signals
329 sigign bitmap of ignored signals
330 sigcatch bitmap of caught signals
331 0 (place holder, used to be the wchan address, use /proc/PID/wchan instead)
334 exit_signal signal to send to parent thread on exit
335 task_cpu which CPU the task is scheduled on
336 rt_priority realtime priority
337 policy scheduling policy (man sched_setscheduler)
338 blkio_ticks time spent waiting for block IO
339 gtime guest time of the task in jiffies
340 cgtime guest time of the task children in jiffies
341 start_data address above which program data+bss is placed
342 end_data address below which program data+bss is placed
343 start_brk address above which program heap can be expanded with brk()
344 arg_start address above which program command line is placed
345 arg_end address below which program command line is placed
346 env_start address above which program environment is placed
347 env_end address below which program environment is placed
348 exit_code the thread's exit_code in the form reported by the waitpid system call
349 ..............................................................................
351 The /proc/PID/maps file containing the currently mapped memory regions and
352 their access permissions.
356 address perms offset dev inode pathname
358 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test
359 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
360 0804a000-0806b000 rw-p 00000000 00:00 0 [heap]
361 a7cb1000-a7cb2000 ---p 00000000 00:00 0
362 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
363 a7eb2000-a7eb3000 ---p 00000000 00:00 0
364 a7eb3000-a7ed5000 rw-p 00000000 00:00 0
365 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
366 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6
367 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6
368 a800b000-a800e000 rw-p 00000000 00:00 0
369 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0
370 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0
371 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0
372 a8024000-a8027000 rw-p 00000000 00:00 0
373 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2
374 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2
375 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2
376 aff35000-aff4a000 rw-p 00000000 00:00 0 [stack]
377 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
379 where "address" is the address space in the process that it occupies, "perms"
380 is a set of permissions:
386 p = private (copy on write)
388 "offset" is the offset into the mapping, "dev" is the device (major:minor), and
389 "inode" is the inode on that device. 0 indicates that no inode is associated
390 with the memory region, as the case would be with BSS (uninitialized data).
391 The "pathname" shows the name associated file for this mapping. If the mapping
392 is not associated with a file:
394 [heap] = the heap of the program
395 [stack] = the stack of the main process
396 [vdso] = the "virtual dynamic shared object",
397 the kernel system call handler
399 or if empty, the mapping is anonymous.
401 The /proc/PID/smaps is an extension based on maps, showing the memory
402 consumption for each of the process's mappings. For each of mappings there
403 is a series of lines such as the following:
405 08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash
419 Private_Hugetlb: 0 kB
425 VmFlags: rd ex mr mw me dw
427 the first of these lines shows the same information as is displayed for the
428 mapping in /proc/PID/maps. The remaining lines show the size of the mapping
429 (size), the amount of the mapping that is currently resident in RAM (RSS), the
430 process' proportional share of this mapping (PSS), the number of clean and
431 dirty private pages in the mapping.
433 The "proportional set size" (PSS) of a process is the count of pages it has
434 in memory, where each page is divided by the number of processes sharing it.
435 So if a process has 1000 pages all to itself, and 1000 shared with one other
436 process, its PSS will be 1500.
437 Note that even a page which is part of a MAP_SHARED mapping, but has only
438 a single pte mapped, i.e. is currently used by only one process, is accounted
439 as private and not as shared.
440 "Referenced" indicates the amount of memory currently marked as referenced or
442 "Anonymous" shows the amount of memory that does not belong to any file. Even
443 a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
444 and a page is modified, the file page is replaced by a private anonymous copy.
445 "LazyFree" shows the amount of memory which is marked by madvise(MADV_FREE).
446 The memory isn't freed immediately with madvise(). It's freed in memory
447 pressure if the memory is clean. Please note that the printed value might
448 be lower than the real value due to optimizations used in the current
449 implementation. If this is not desirable please file a bug report.
450 "AnonHugePages" shows the ammount of memory backed by transparent hugepage.
451 "ShmemPmdMapped" shows the ammount of shared (shmem/tmpfs) memory backed by
453 "Shared_Hugetlb" and "Private_Hugetlb" show the ammounts of memory backed by
454 hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
455 reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
456 "Swap" shows how much would-be-anonymous memory is also used, but out on swap.
457 For shmem mappings, "Swap" includes also the size of the mapped (and not
458 replaced by copy-on-write) part of the underlying shmem object out on swap.
459 "SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
460 does not take into account swapped out page of underlying shmem objects.
461 "Locked" indicates whether the mapping is locked in memory or not.
463 "VmFlags" field deserves a separate description. This member represents the kernel
464 flags associated with the particular virtual memory area in two letter encoded
465 manner. The codes are the following:
474 gd - stack segment growns down
476 dw - disabled write to the mapped file
477 lo - pages are locked in memory
478 io - memory mapped I/O area
479 sr - sequential read advise provided
480 rr - random read advise provided
481 dc - do not copy area on fork
482 de - do not expand area on remapping
483 ac - area is accountable
484 nr - swap space is not reserved for the area
485 ht - area uses huge tlb pages
486 ar - architecture specific flag
487 dd - do not include area into core dump
490 hg - huge page advise flag
491 nh - no-huge page advise flag
492 mg - mergable advise flag
494 Note that there is no guarantee that every flag and associated mnemonic will
495 be present in all further kernel releases. Things get changed, the flags may
496 be vanished or the reverse -- new added.
498 This file is only present if the CONFIG_MMU kernel configuration option is
501 Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent
502 output can be achieved only in the single read call).
503 This typically manifests when doing partial reads of these files while the
504 memory map is being modified. Despite the races, we do provide the following
507 1) The mapped addresses never go backwards, which implies no two
508 regions will ever overlap.
509 2) If there is something at a given vaddr during the entirety of the
510 life of the smaps/maps walk, there will be some output for it.
513 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
514 bits on both physical and virtual pages associated with a process, and the
515 soft-dirty bit on pte (see Documentation/vm/soft-dirty.txt for details).
516 To clear the bits for all the pages associated with the process
517 > echo 1 > /proc/PID/clear_refs
519 To clear the bits for the anonymous pages associated with the process
520 > echo 2 > /proc/PID/clear_refs
522 To clear the bits for the file mapped pages associated with the process
523 > echo 3 > /proc/PID/clear_refs
525 To clear the soft-dirty bit
526 > echo 4 > /proc/PID/clear_refs
528 To reset the peak resident set size ("high water mark") to the process's
530 > echo 5 > /proc/PID/clear_refs
532 Any other value written to /proc/PID/clear_refs will have no effect.
534 The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
535 using /proc/kpageflags and number of times a page is mapped using
536 /proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
538 The /proc/pid/numa_maps is an extension based on maps, showing the memory
539 locality and binding policy, as well as the memory usage (in pages) of
540 each mapping. The output follows a general format where mapping details get
541 summarized separated by blank spaces, one mapping per each file line:
543 address policy mapping details
545 00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
546 00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
547 3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
548 320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
549 3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
550 3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
551 3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
552 320698b000 default file=/lib64/libc-2.12.so
553 3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
554 3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
555 3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
556 7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
557 7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
558 7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
559 7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
560 7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
563 "address" is the starting address for the mapping;
564 "policy" reports the NUMA memory policy set for the mapping (see vm/numa_memory_policy.txt);
565 "mapping details" summarizes mapping data such as mapping type, page usage counters,
566 node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
567 size, in KB, that is backing the mapping up.
572 Similar to the process entries, the kernel data files give information about
573 the running kernel. The files used to obtain this information are contained in
574 /proc and are listed in Table 1-5. Not all of these will be present in your
575 system. It depends on the kernel configuration and the loaded modules, which
576 files are there, and which are missing.
578 Table 1-5: Kernel info in /proc
579 ..............................................................................
581 apm Advanced power management info
582 buddyinfo Kernel memory allocator information (see text) (2.5)
583 bus Directory containing bus specific information
584 cmdline Kernel command line
585 cpuinfo Info about the CPU
586 devices Available devices (block and character)
587 dma Used DMS channels
588 filesystems Supported filesystems
589 driver Various drivers grouped here, currently rtc (2.4)
590 execdomains Execdomains, related to security (2.4)
591 fb Frame Buffer devices (2.4)
592 fs File system parameters, currently nfs/exports (2.4)
593 ide Directory containing info about the IDE subsystem
594 interrupts Interrupt usage
595 iomem Memory map (2.4)
596 ioports I/O port usage
597 irq Masks for irq to cpu affinity (2.4)(smp?)
598 isapnp ISA PnP (Plug&Play) Info (2.4)
599 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
601 ksyms Kernel symbol table
602 loadavg Load average of last 1, 5 & 15 minutes
606 modules List of loaded modules
607 mounts Mounted filesystems
608 net Networking info (see text)
609 pagetypeinfo Additional page allocator information (see text) (2.5)
610 partitions Table of partitions known to the system
611 pci Deprecated info of PCI bus (new way -> /proc/bus/pci/,
612 decoupled by lspci (2.4)
614 scsi SCSI info (see text)
615 slabinfo Slab pool info
616 softirqs softirq usage
617 stat Overall statistics
618 swaps Swap space utilization
620 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4)
621 tty Info of tty drivers
622 uptime Wall clock since boot, combined idle time of all cpus
623 version Kernel version
624 video bttv info of video resources (2.4)
625 vmallocinfo Show vmalloced areas
626 ..............................................................................
628 You can, for example, check which interrupts are currently in use and what
629 they are used for by looking in the file /proc/interrupts:
631 > cat /proc/interrupts
633 0: 8728810 XT-PIC timer
634 1: 895 XT-PIC keyboard
636 3: 531695 XT-PIC aha152x
637 4: 2014133 XT-PIC serial
638 5: 44401 XT-PIC pcnet_cs
641 12: 182918 XT-PIC PS/2 Mouse
643 14: 1232265 XT-PIC ide0
647 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
648 output of a SMP machine):
650 > cat /proc/interrupts
653 0: 1243498 1214548 IO-APIC-edge timer
654 1: 8949 8958 IO-APIC-edge keyboard
655 2: 0 0 XT-PIC cascade
656 5: 11286 10161 IO-APIC-edge soundblaster
657 8: 1 0 IO-APIC-edge rtc
658 9: 27422 27407 IO-APIC-edge 3c503
659 12: 113645 113873 IO-APIC-edge PS/2 Mouse
661 14: 22491 24012 IO-APIC-edge ide0
662 15: 2183 2415 IO-APIC-edge ide1
663 17: 30564 30414 IO-APIC-level eth0
664 18: 177 164 IO-APIC-level bttv
669 NMI is incremented in this case because every timer interrupt generates a NMI
670 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
672 LOC is the local interrupt counter of the internal APIC of every CPU.
674 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
675 connects the CPUs in a SMP system. This means that an error has been detected,
676 the IO-APIC automatically retry the transmission, so it should not be a big
677 problem, but you should read the SMP-FAQ.
679 In 2.6.2* /proc/interrupts was expanded again. This time the goal was for
680 /proc/interrupts to display every IRQ vector in use by the system, not
681 just those considered 'most important'. The new vectors are:
683 THR -- interrupt raised when a machine check threshold counter
684 (typically counting ECC corrected errors of memory or cache) exceeds
685 a configurable threshold. Only available on some systems.
687 TRM -- a thermal event interrupt occurs when a temperature threshold
688 has been exceeded for the CPU. This interrupt may also be generated
689 when the temperature drops back to normal.
691 SPU -- a spurious interrupt is some interrupt that was raised then lowered
692 by some IO device before it could be fully processed by the APIC. Hence
693 the APIC sees the interrupt but does not know what device it came from.
694 For this case the APIC will generate the interrupt with a IRQ vector
695 of 0xff. This might also be generated by chipset bugs.
697 RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
698 sent from one CPU to another per the needs of the OS. Typically,
699 their statistics are used by kernel developers and interested users to
700 determine the occurrence of interrupts of the given type.
702 The above IRQ vectors are displayed only when relevant. For example,
703 the threshold vector does not exist on x86_64 platforms. Others are
704 suppressed when the system is a uniprocessor. As of this writing, only
705 i386 and x86_64 platforms support the new IRQ vector displays.
707 Of some interest is the introduction of the /proc/irq directory to 2.4.
708 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
709 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
710 irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
715 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask
716 1 11 13 15 17 19 3 5 7 9 default_smp_affinity
720 smp_affinity is a bitmask, in which you can specify which CPUs can handle the
721 IRQ, you can set it by doing:
723 > echo 1 > /proc/irq/10/smp_affinity
725 This means that only the first CPU will handle the IRQ, but you can also echo
726 5 which means that only the first and third CPU can handle the IRQ.
728 The contents of each smp_affinity file is the same by default:
730 > cat /proc/irq/0/smp_affinity
733 There is an alternate interface, smp_affinity_list which allows specifying
734 a cpu range instead of a bitmask:
736 > cat /proc/irq/0/smp_affinity_list
739 The default_smp_affinity mask applies to all non-active IRQs, which are the
740 IRQs which have not yet been allocated/activated, and hence which lack a
741 /proc/irq/[0-9]* directory.
743 The node file on an SMP system shows the node to which the device using the IRQ
744 reports itself as being attached. This hardware locality information does not
745 include information about any possible driver locality preference.
747 prof_cpu_mask specifies which CPUs are to be profiled by the system wide
748 profiler. Default value is ffffffff (all cpus if there are only 32 of them).
750 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
751 between all the CPUs which are allowed to handle it. As usual the kernel has
752 more info than you and does a better job than you, so the defaults are the
753 best choice for almost everyone. [Note this applies only to those IO-APIC's
754 that support "Round Robin" interrupt distribution.]
756 There are three more important subdirectories in /proc: net, scsi, and sys.
757 The general rule is that the contents, or even the existence of these
758 directories, depend on your kernel configuration. If SCSI is not enabled, the
759 directory scsi may not exist. The same is true with the net, which is there
760 only when networking support is present in the running kernel.
762 The slabinfo file gives information about memory usage at the slab level.
763 Linux uses slab pools for memory management above page level in version 2.2.
764 Commonly used objects have their own slab pool (such as network buffers,
765 directory cache, and so on).
767 ..............................................................................
769 > cat /proc/buddyinfo
771 Node 0, zone DMA 0 4 5 4 4 3 ...
772 Node 0, zone Normal 1 0 0 1 101 8 ...
773 Node 0, zone HighMem 2 0 0 1 1 0 ...
775 External fragmentation is a problem under some workloads, and buddyinfo is a
776 useful tool for helping diagnose these problems. Buddyinfo will give you a
777 clue as to how big an area you can safely allocate, or why a previous
780 Each column represents the number of pages of a certain order which are
781 available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
782 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
783 available in ZONE_NORMAL, etc...
785 More information relevant to external fragmentation can be found in
788 > cat /proc/pagetypeinfo
792 Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10
793 Node 0, zone DMA, type Unmovable 0 0 0 1 1 1 1 1 1 1 0
794 Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0
795 Node 0, zone DMA, type Movable 1 1 2 1 2 1 1 0 1 0 2
796 Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 1 0
797 Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0
798 Node 0, zone DMA32, type Unmovable 103 54 77 1 1 1 11 8 7 1 9
799 Node 0, zone DMA32, type Reclaimable 0 0 2 1 0 0 0 0 1 0 0
800 Node 0, zone DMA32, type Movable 169 152 113 91 77 54 39 13 6 1 452
801 Node 0, zone DMA32, type Reserve 1 2 2 2 2 0 1 1 1 1 0
802 Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0
804 Number of blocks type Unmovable Reclaimable Movable Reserve Isolate
805 Node 0, zone DMA 2 0 5 1 0
806 Node 0, zone DMA32 41 6 967 2 0
808 Fragmentation avoidance in the kernel works by grouping pages of different
809 migrate types into the same contiguous regions of memory called page blocks.
810 A page block is typically the size of the default hugepage size e.g. 2MB on
811 X86-64. By keeping pages grouped based on their ability to move, the kernel
812 can reclaim pages within a page block to satisfy a high-order allocation.
814 The pagetypinfo begins with information on the size of a page block. It
815 then gives the same type of information as buddyinfo except broken down
816 by migrate-type and finishes with details on how many page blocks of each
819 If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
820 from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can
821 make an estimate of the likely number of huge pages that can be allocated
822 at a given point in time. All the "Movable" blocks should be allocatable
823 unless memory has been mlock()'d. Some of the Reclaimable blocks should
824 also be allocatable although a lot of filesystem metadata may have to be
825 reclaimed to achieve this.
827 ..............................................................................
831 Provides information about distribution and utilization of memory. This
832 varies by architecture and compile options. The following is from a
833 16GB PIII, which has highmem enabled. You may not have all of these fields.
837 MemTotal: 16344972 kB
839 MemAvailable: 14836172 kB
845 HighTotal: 15597528 kB
846 HighFree: 13629632 kB
857 SReclaimable: 159856 kB
858 SUnreclaim: 124508 kB
863 CommitLimit: 7669796 kB
864 Committed_AS: 100056 kB
865 VmallocTotal: 112216 kB
867 VmallocChunk: 111088 kB
868 AnonHugePages: 49152 kB
873 MemTotal: Total usable ram (i.e. physical ram minus a few reserved
874 bits and the kernel binary code)
875 MemFree: The sum of LowFree+HighFree
876 MemAvailable: An estimate of how much memory is available for starting new
877 applications, without swapping. Calculated from MemFree,
878 SReclaimable, the size of the file LRU lists, and the low
879 watermarks in each zone.
880 The estimate takes into account that the system needs some
881 page cache to function well, and that not all reclaimable
882 slab will be reclaimable, due to items being in use. The
883 impact of those factors will vary from system to system.
884 Buffers: Relatively temporary storage for raw disk blocks
885 shouldn't get tremendously large (20MB or so)
886 Cached: in-memory cache for files read from the disk (the
887 pagecache). Doesn't include SwapCached
888 SwapCached: Memory that once was swapped out, is swapped back in but
889 still also is in the swapfile (if memory is needed it
890 doesn't need to be swapped out AGAIN because it is already
891 in the swapfile. This saves I/O)
892 Active: Memory that has been used more recently and usually not
893 reclaimed unless absolutely necessary.
894 Inactive: Memory which has been less recently used. It is more
895 eligible to be reclaimed for other purposes
897 HighFree: Highmem is all memory above ~860MB of physical memory
898 Highmem areas are for use by userspace programs, or
899 for the pagecache. The kernel must use tricks to access
900 this memory, making it slower to access than lowmem.
902 LowFree: Lowmem is memory which can be used for everything that
903 highmem can be used for, but it is also available for the
904 kernel's use for its own data structures. Among many
905 other things, it is where everything from the Slab is
906 allocated. Bad things happen when you're out of lowmem.
907 SwapTotal: total amount of swap space available
908 SwapFree: Memory which has been evicted from RAM, and is temporarily
910 Dirty: Memory which is waiting to get written back to the disk
911 Writeback: Memory which is actively being written back to the disk
912 AnonPages: Non-file backed pages mapped into userspace page tables
913 AnonHugePages: Non-file backed huge pages mapped into userspace page tables
914 Mapped: files which have been mmaped, such as libraries
915 Shmem: Total memory used by shared memory (shmem) and tmpfs
916 ShmemHugePages: Memory used by shared memory (shmem) and tmpfs allocated
918 ShmemPmdMapped: Shared memory mapped into userspace with huge pages
919 Slab: in-kernel data structures cache
920 SReclaimable: Part of Slab, that might be reclaimed, such as caches
921 SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
922 PageTables: amount of memory dedicated to the lowest level of page
924 NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
926 Bounce: Memory used for block device "bounce buffers"
927 WritebackTmp: Memory used by FUSE for temporary writeback buffers
928 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
929 this is the total amount of memory currently available to
930 be allocated on the system. This limit is only adhered to
931 if strict overcommit accounting is enabled (mode 2 in
932 'vm.overcommit_memory').
933 The CommitLimit is calculated with the following formula:
934 CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
935 overcommit_ratio / 100 + [total swap pages]
936 For example, on a system with 1G of physical RAM and 7G
937 of swap with a `vm.overcommit_ratio` of 30 it would
938 yield a CommitLimit of 7.3G.
939 For more details, see the memory overcommit documentation
940 in vm/overcommit-accounting.
941 Committed_AS: The amount of memory presently allocated on the system.
942 The committed memory is a sum of all of the memory which
943 has been allocated by processes, even if it has not been
944 "used" by them as of yet. A process which malloc()'s 1G
945 of memory, but only touches 300M of it will show up as
946 using 1G. This 1G is memory which has been "committed" to
947 by the VM and can be used at any time by the allocating
948 application. With strict overcommit enabled on the system
949 (mode 2 in 'vm.overcommit_memory'),allocations which would
950 exceed the CommitLimit (detailed above) will not be permitted.
951 This is useful if one needs to guarantee that processes will
952 not fail due to lack of memory once that memory has been
953 successfully allocated.
954 VmallocTotal: total size of vmalloc memory area
955 VmallocUsed: amount of vmalloc area which is used
956 VmallocChunk: largest contiguous block of vmalloc area which is free
958 ..............................................................................
962 Provides information about vmalloced/vmaped areas. One line per area,
963 containing the virtual address range of the area, size in bytes,
964 caller information of the creator, and optional information depending
965 on the kind of area :
967 pages=nr number of pages
968 phys=addr if a physical address was specified
969 ioremap I/O mapping (ioremap() and friends)
970 vmalloc vmalloc() area
973 vpages buffer for pages pointers was vmalloced (huge area)
974 N<node>=nr (Only on NUMA kernels)
975 Number of pages allocated on memory node <node>
977 > cat /proc/vmallocinfo
978 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
979 /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
980 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
981 /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
982 0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f...
983 phys=7fee8000 ioremap
984 0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f...
985 phys=7fee7000 ioremap
986 0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210
987 0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ...
988 /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
989 0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ...
991 0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ...
992 /0x130 [x_tables] pages=4 vmalloc N0=4
993 0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ...
994 pages=14 vmalloc N2=14
995 0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ...
997 0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ...
999 0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ...
1000 pages=10 vmalloc N0=10
1002 ..............................................................................
1006 Provides counts of softirq handlers serviced since boot time, for each cpu.
1008 > cat /proc/softirqs
1011 TIMER: 27166 27120 27097 27034
1016 SCHED: 27035 26983 26971 26746
1018 RCU: 1678 1769 2178 2250
1021 1.3 IDE devices in /proc/ide
1022 ----------------------------
1024 The subdirectory /proc/ide contains information about all IDE devices of which
1025 the kernel is aware. There is one subdirectory for each IDE controller, the
1026 file drivers and a link for each IDE device, pointing to the device directory
1027 in the controller specific subtree.
1029 The file drivers contains general information about the drivers used for the
1032 > cat /proc/ide/drivers
1033 ide-cdrom version 4.53
1034 ide-disk version 1.08
1036 More detailed information can be found in the controller specific
1037 subdirectories. These are named ide0, ide1 and so on. Each of these
1038 directories contains the files shown in table 1-6.
1041 Table 1-6: IDE controller info in /proc/ide/ide?
1042 ..............................................................................
1044 channel IDE channel (0 or 1)
1045 config Configuration (only for PCI/IDE bridge)
1047 model Type/Chipset of IDE controller
1048 ..............................................................................
1050 Each device connected to a controller has a separate subdirectory in the
1051 controllers directory. The files listed in table 1-7 are contained in these
1055 Table 1-7: IDE device information
1056 ..............................................................................
1059 capacity Capacity of the medium (in 512Byte blocks)
1060 driver driver and version
1061 geometry physical and logical geometry
1062 identify device identify block
1064 model device identifier
1065 settings device setup
1066 smart_thresholds IDE disk management thresholds
1067 smart_values IDE disk management values
1068 ..............................................................................
1070 The most interesting file is settings. This file contains a nice overview of
1071 the drive parameters:
1073 # cat /proc/ide/ide0/hda/settings
1074 name value min max mode
1075 ---- ----- --- --- ----
1076 bios_cyl 526 0 65535 rw
1077 bios_head 255 0 255 rw
1078 bios_sect 63 0 63 rw
1079 breada_readahead 4 0 127 rw
1081 file_readahead 72 0 2097151 rw
1083 keepsettings 0 0 1 rw
1084 max_kb_per_request 122 1 127 rw
1088 pio_mode write-only 0 255 w
1094 1.4 Networking info in /proc/net
1095 --------------------------------
1097 The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the
1098 additional values you get for IP version 6 if you configure the kernel to
1099 support this. Table 1-9 lists the files and their meaning.
1102 Table 1-8: IPv6 info in /proc/net
1103 ..............................................................................
1105 udp6 UDP sockets (IPv6)
1106 tcp6 TCP sockets (IPv6)
1107 raw6 Raw device statistics (IPv6)
1108 igmp6 IP multicast addresses, which this host joined (IPv6)
1109 if_inet6 List of IPv6 interface addresses
1110 ipv6_route Kernel routing table for IPv6
1111 rt6_stats Global IPv6 routing tables statistics
1112 sockstat6 Socket statistics (IPv6)
1113 snmp6 Snmp data (IPv6)
1114 ..............................................................................
1117 Table 1-9: Network info in /proc/net
1118 ..............................................................................
1120 arp Kernel ARP table
1121 dev network devices with statistics
1122 dev_mcast the Layer2 multicast groups a device is listening too
1123 (interface index, label, number of references, number of bound
1125 dev_stat network device status
1126 ip_fwchains Firewall chain linkage
1127 ip_fwnames Firewall chain names
1128 ip_masq Directory containing the masquerading tables
1129 ip_masquerade Major masquerading table
1130 netstat Network statistics
1131 raw raw device statistics
1132 route Kernel routing table
1133 rpc Directory containing rpc info
1134 rt_cache Routing cache
1136 sockstat Socket statistics
1139 unix UNIX domain sockets
1140 wireless Wireless interface data (Wavelan etc)
1141 igmp IP multicast addresses, which this host joined
1142 psched Global packet scheduler parameters.
1143 netlink List of PF_NETLINK sockets
1144 ip_mr_vifs List of multicast virtual interfaces
1145 ip_mr_cache List of multicast routing cache
1146 ..............................................................................
1148 You can use this information to see which network devices are available in
1149 your system and how much traffic was routed over those devices:
1152 Inter-|Receive |[...
1153 face |bytes packets errs drop fifo frame compressed multicast|[...
1154 lo: 908188 5596 0 0 0 0 0 0 [...
1155 ppp0:15475140 20721 410 0 0 410 0 0 [...
1156 eth0: 614530 7085 0 0 0 0 0 1 [...
1159 ...] bytes packets errs drop fifo colls carrier compressed
1160 ...] 908188 5596 0 0 0 0 0 0
1161 ...] 1375103 17405 0 0 0 0 0 0
1162 ...] 1703981 5535 0 0 0 3 0 0
1164 In addition, each Channel Bond interface has its own directory. For
1165 example, the bond0 device will have a directory called /proc/net/bond0/.
1166 It will contain information that is specific to that bond, such as the
1167 current slaves of the bond, the link status of the slaves, and how
1168 many times the slaves link has failed.
1173 If you have a SCSI host adapter in your system, you'll find a subdirectory
1174 named after the driver for this adapter in /proc/scsi. You'll also see a list
1175 of all recognized SCSI devices in /proc/scsi:
1177 >cat /proc/scsi/scsi
1179 Host: scsi0 Channel: 00 Id: 00 Lun: 00
1180 Vendor: IBM Model: DGHS09U Rev: 03E0
1181 Type: Direct-Access ANSI SCSI revision: 03
1182 Host: scsi0 Channel: 00 Id: 06 Lun: 00
1183 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04
1184 Type: CD-ROM ANSI SCSI revision: 02
1187 The directory named after the driver has one file for each adapter found in
1188 the system. These files contain information about the controller, including
1189 the used IRQ and the IO address range. The amount of information shown is
1190 dependent on the adapter you use. The example shows the output for an Adaptec
1191 AHA-2940 SCSI adapter:
1193 > cat /proc/scsi/aic7xxx/0
1195 Adaptec AIC7xxx driver version: 5.1.19/3.2.4
1197 TCQ Enabled By Default : Disabled
1198 AIC7XXX_PROC_STATS : Disabled
1199 AIC7XXX_RESET_DELAY : 5
1200 Adapter Configuration:
1201 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
1202 Ultra Wide Controller
1203 PCI MMAPed I/O Base: 0xeb001000
1204 Adapter SEEPROM Config: SEEPROM found and used.
1205 Adaptec SCSI BIOS: Enabled
1207 SCBs: Active 0, Max Active 2,
1208 Allocated 15, HW 16, Page 255
1210 BIOS Control Word: 0x18b6
1211 Adapter Control Word: 0x005b
1212 Extended Translation: Enabled
1213 Disconnect Enable Flags: 0xffff
1214 Ultra Enable Flags: 0x0001
1215 Tag Queue Enable Flags: 0x0000
1216 Ordered Queue Tag Flags: 0x0000
1217 Default Tag Queue Depth: 8
1218 Tagged Queue By Device array for aic7xxx host instance 0:
1219 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
1220 Actual queue depth per device for aic7xxx host instance 0:
1221 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
1224 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
1225 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
1226 Total transfers 160151 (74577 reads and 85574 writes)
1228 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
1229 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
1230 Total transfers 0 (0 reads and 0 writes)
1233 1.6 Parallel port info in /proc/parport
1234 ---------------------------------------
1236 The directory /proc/parport contains information about the parallel ports of
1237 your system. It has one subdirectory for each port, named after the port
1240 These directories contain the four files shown in Table 1-10.
1243 Table 1-10: Files in /proc/parport
1244 ..............................................................................
1246 autoprobe Any IEEE-1284 device ID information that has been acquired.
1247 devices list of the device drivers using that port. A + will appear by the
1248 name of the device currently using the port (it might not appear
1250 hardware Parallel port's base address, IRQ line and DMA channel.
1251 irq IRQ that parport is using for that port. This is in a separate
1252 file to allow you to alter it by writing a new value in (IRQ
1254 ..............................................................................
1256 1.7 TTY info in /proc/tty
1257 -------------------------
1259 Information about the available and actually used tty's can be found in the
1260 directory /proc/tty.You'll find entries for drivers and line disciplines in
1261 this directory, as shown in Table 1-11.
1264 Table 1-11: Files in /proc/tty
1265 ..............................................................................
1267 drivers list of drivers and their usage
1268 ldiscs registered line disciplines
1269 driver/serial usage statistic and status of single tty lines
1270 ..............................................................................
1272 To see which tty's are currently in use, you can simply look into the file
1275 > cat /proc/tty/drivers
1276 pty_slave /dev/pts 136 0-255 pty:slave
1277 pty_master /dev/ptm 128 0-255 pty:master
1278 pty_slave /dev/ttyp 3 0-255 pty:slave
1279 pty_master /dev/pty 2 0-255 pty:master
1280 serial /dev/cua 5 64-67 serial:callout
1281 serial /dev/ttyS 4 64-67 serial
1282 /dev/tty0 /dev/tty0 4 0 system:vtmaster
1283 /dev/ptmx /dev/ptmx 5 2 system
1284 /dev/console /dev/console 5 1 system:console
1285 /dev/tty /dev/tty 5 0 system:/dev/tty
1286 unknown /dev/tty 4 1-63 console
1289 1.8 Miscellaneous kernel statistics in /proc/stat
1290 -------------------------------------------------
1292 Various pieces of information about kernel activity are available in the
1293 /proc/stat file. All of the numbers reported in this file are aggregates
1294 since the system first booted. For a quick look, simply cat the file:
1297 cpu 2255 34 2290 22625563 6290 127 456 0 0 0
1298 cpu0 1132 34 1441 11311718 3675 127 438 0 0 0
1299 cpu1 1123 0 849 11313845 2614 0 18 0 0 0
1300 intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1306 softirq 183433 0 21755 12 39 1137 231 21459 2263
1308 The very first "cpu" line aggregates the numbers in all of the other "cpuN"
1309 lines. These numbers identify the amount of time the CPU has spent performing
1310 different kinds of work. Time units are in USER_HZ (typically hundredths of a
1311 second). The meanings of the columns are as follows, from left to right:
1313 - user: normal processes executing in user mode
1314 - nice: niced processes executing in user mode
1315 - system: processes executing in kernel mode
1316 - idle: twiddling thumbs
1317 - iowait: In a word, iowait stands for waiting for I/O to complete. But there
1318 are several problems:
1319 1. Cpu will not wait for I/O to complete, iowait is the time that a task is
1320 waiting for I/O to complete. When cpu goes into idle state for
1321 outstanding task io, another task will be scheduled on this CPU.
1322 2. In a multi-core CPU, the task waiting for I/O to complete is not running
1323 on any CPU, so the iowait of each CPU is difficult to calculate.
1324 3. The value of iowait field in /proc/stat will decrease in certain
1326 So, the iowait is not reliable by reading from /proc/stat.
1327 - irq: servicing interrupts
1328 - softirq: servicing softirqs
1329 - steal: involuntary wait
1330 - guest: running a normal guest
1331 - guest_nice: running a niced guest
1333 The "intr" line gives counts of interrupts serviced since boot time, for each
1334 of the possible system interrupts. The first column is the total of all
1335 interrupts serviced including unnumbered architecture specific interrupts;
1336 each subsequent column is the total for that particular numbered interrupt.
1337 Unnumbered interrupts are not shown, only summed into the total.
1339 The "ctxt" line gives the total number of context switches across all CPUs.
1341 The "btime" line gives the time at which the system booted, in seconds since
1344 The "processes" line gives the number of processes and threads created, which
1345 includes (but is not limited to) those created by calls to the fork() and
1346 clone() system calls.
1348 The "procs_running" line gives the total number of threads that are
1349 running or ready to run (i.e., the total number of runnable threads).
1351 The "procs_blocked" line gives the number of processes currently blocked,
1352 waiting for I/O to complete.
1354 The "softirq" line gives counts of softirqs serviced since boot time, for each
1355 of the possible system softirqs. The first column is the total of all
1356 softirqs serviced; each subsequent column is the total for that particular
1360 1.9 Ext4 file system parameters
1361 -------------------------------
1363 Information about mounted ext4 file systems can be found in
1364 /proc/fs/ext4. Each mounted filesystem will have a directory in
1365 /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1366 /proc/fs/ext4/dm-0). The files in each per-device directory are shown
1367 in Table 1-12, below.
1369 Table 1-12: Files in /proc/fs/ext4/<devname>
1370 ..............................................................................
1372 mb_groups details of multiblock allocator buddy cache of free blocks
1373 ..............................................................................
1377 Shows registered system console lines.
1379 To see which character device lines are currently used for the system console
1380 /dev/console, you may simply look into the file /proc/consoles:
1382 > cat /proc/consoles
1388 device name of the device
1389 operations R = can do read operations
1390 W = can do write operations
1392 flags E = it is enabled
1393 C = it is preferred console
1394 B = it is primary boot console
1395 p = it is used for printk buffer
1396 b = it is not a TTY but a Braille device
1397 a = it is safe to use when cpu is offline
1398 major:minor major and minor number of the device separated by a colon
1400 ------------------------------------------------------------------------------
1402 ------------------------------------------------------------------------------
1403 The /proc file system serves information about the running system. It not only
1404 allows access to process data but also allows you to request the kernel status
1405 by reading files in the hierarchy.
1407 The directory structure of /proc reflects the types of information and makes
1408 it easy, if not obvious, where to look for specific data.
1409 ------------------------------------------------------------------------------
1411 ------------------------------------------------------------------------------
1412 CHAPTER 2: MODIFYING SYSTEM PARAMETERS
1413 ------------------------------------------------------------------------------
1415 ------------------------------------------------------------------------------
1417 ------------------------------------------------------------------------------
1418 * Modifying kernel parameters by writing into files found in /proc/sys
1419 * Exploring the files which modify certain parameters
1420 * Review of the /proc/sys file tree
1421 ------------------------------------------------------------------------------
1424 A very interesting part of /proc is the directory /proc/sys. This is not only
1425 a source of information, it also allows you to change parameters within the
1426 kernel. Be very careful when attempting this. You can optimize your system,
1427 but you can also cause it to crash. Never alter kernel parameters on a
1428 production system. Set up a development machine and test to make sure that
1429 everything works the way you want it to. You may have no alternative but to
1430 reboot the machine once an error has been made.
1432 To change a value, simply echo the new value into the file. An example is
1433 given below in the section on the file system data. You need to be root to do
1434 this. You can create your own boot script to perform this every time your
1437 The files in /proc/sys can be used to fine tune and monitor miscellaneous and
1438 general things in the operation of the Linux kernel. Since some of the files
1439 can inadvertently disrupt your system, it is advisable to read both
1440 documentation and source before actually making adjustments. In any case, be
1441 very careful when writing to any of these files. The entries in /proc may
1442 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1443 review the kernel documentation in the directory /usr/src/linux/Documentation.
1444 This chapter is heavily based on the documentation included in the pre 2.2
1445 kernels, and became part of it in version 2.2.1 of the Linux kernel.
1447 Please see: Documentation/sysctl/ directory for descriptions of these
1450 ------------------------------------------------------------------------------
1452 ------------------------------------------------------------------------------
1453 Certain aspects of kernel behavior can be modified at runtime, without the
1454 need to recompile the kernel, or even to reboot the system. The files in the
1455 /proc/sys tree can not only be read, but also modified. You can use the echo
1456 command to write value into these files, thereby changing the default settings
1458 ------------------------------------------------------------------------------
1460 ------------------------------------------------------------------------------
1461 CHAPTER 3: PER-PROCESS PARAMETERS
1462 ------------------------------------------------------------------------------
1464 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1465 --------------------------------------------------------------------------------
1467 These file can be used to adjust the badness heuristic used to select which
1468 process gets killed in out of memory conditions.
1470 The badness heuristic assigns a value to each candidate task ranging from 0
1471 (never kill) to 1000 (always kill) to determine which process is targeted. The
1472 units are roughly a proportion along that range of allowed memory the process
1473 may allocate from based on an estimation of its current memory and swap use.
1474 For example, if a task is using all allowed memory, its badness score will be
1475 1000. If it is using half of its allowed memory, its score will be 500.
1477 There is an additional factor included in the badness score: the current memory
1478 and swap usage is discounted by 3% for root processes.
1480 The amount of "allowed" memory depends on the context in which the oom killer
1481 was called. If it is due to the memory assigned to the allocating task's cpuset
1482 being exhausted, the allowed memory represents the set of mems assigned to that
1483 cpuset. If it is due to a mempolicy's node(s) being exhausted, the allowed
1484 memory represents the set of mempolicy nodes. If it is due to a memory
1485 limit (or swap limit) being reached, the allowed memory is that configured
1486 limit. Finally, if it is due to the entire system being out of memory, the
1487 allowed memory represents all allocatable resources.
1489 The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1490 is used to determine which task to kill. Acceptable values range from -1000
1491 (OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This allows userspace to
1492 polarize the preference for oom killing either by always preferring a certain
1493 task or completely disabling it. The lowest possible value, -1000, is
1494 equivalent to disabling oom killing entirely for that task since it will always
1495 report a badness score of 0.
1497 Consequently, it is very simple for userspace to define the amount of memory to
1498 consider for each task. Setting a /proc/<pid>/oom_score_adj value of +500, for
1499 example, is roughly equivalent to allowing the remainder of tasks sharing the
1500 same system, cpuset, mempolicy, or memory controller resources to use at least
1501 50% more memory. A value of -500, on the other hand, would be roughly
1502 equivalent to discounting 50% of the task's allowed memory from being considered
1503 as scoring against the task.
1505 For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1506 be used to tune the badness score. Its acceptable values range from -16
1507 (OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1508 (OOM_DISABLE) to disable oom killing entirely for that task. Its value is
1509 scaled linearly with /proc/<pid>/oom_score_adj.
1511 The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1512 value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1513 requires CAP_SYS_RESOURCE.
1515 Caveat: when a parent task is selected, the oom killer will sacrifice any first
1516 generation children with separate address spaces instead, if possible. This
1517 avoids servers and important system daemons from being killed and loses the
1518 minimal amount of work.
1521 3.2 /proc/<pid>/oom_score - Display current oom-killer score
1522 -------------------------------------------------------------
1524 This file can be used to check the current score used by the oom-killer is for
1525 any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1526 process should be killed in an out-of-memory situation.
1529 3.3 /proc/<pid>/io - Display the IO accounting fields
1530 -------------------------------------------------------
1532 This file contains IO statistics for each running process
1537 test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1540 test:/tmp # cat /proc/3828/io
1546 write_bytes: 323932160
1547 cancelled_write_bytes: 0
1556 I/O counter: chars read
1557 The number of bytes which this task has caused to be read from storage. This
1558 is simply the sum of bytes which this process passed to read() and pread().
1559 It includes things like tty IO and it is unaffected by whether or not actual
1560 physical disk IO was required (the read might have been satisfied from
1567 I/O counter: chars written
1568 The number of bytes which this task has caused, or shall cause to be written
1569 to disk. Similar caveats apply here as with rchar.
1575 I/O counter: read syscalls
1576 Attempt to count the number of read I/O operations, i.e. syscalls like read()
1583 I/O counter: write syscalls
1584 Attempt to count the number of write I/O operations, i.e. syscalls like
1585 write() and pwrite().
1591 I/O counter: bytes read
1592 Attempt to count the number of bytes which this process really did cause to
1593 be fetched from the storage layer. Done at the submit_bio() level, so it is
1594 accurate for block-backed filesystems. <please add status regarding NFS and
1595 CIFS at a later time>
1601 I/O counter: bytes written
1602 Attempt to count the number of bytes which this process caused to be sent to
1603 the storage layer. This is done at page-dirtying time.
1606 cancelled_write_bytes
1607 ---------------------
1609 The big inaccuracy here is truncate. If a process writes 1MB to a file and
1610 then deletes the file, it will in fact perform no writeout. But it will have
1611 been accounted as having caused 1MB of write.
1612 In other words: The number of bytes which this process caused to not happen,
1613 by truncating pagecache. A task can cause "negative" IO too. If this task
1614 truncates some dirty pagecache, some IO which another task has been accounted
1615 for (in its write_bytes) will not be happening. We _could_ just subtract that
1616 from the truncating task's write_bytes, but there is information loss in doing
1623 At its current implementation state, this is a bit racy on 32-bit machines: if
1624 process A reads process B's /proc/pid/io while process B is updating one of
1625 those 64-bit counters, process A could see an intermediate result.
1628 More information about this can be found within the taskstats documentation in
1629 Documentation/accounting.
1631 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1632 ---------------------------------------------------------------
1633 When a process is dumped, all anonymous memory is written to a core file as
1634 long as the size of the core file isn't limited. But sometimes we don't want
1635 to dump some memory segments, for example, huge shared memory or DAX.
1636 Conversely, sometimes we want to save file-backed memory segments into a core
1637 file, not only the individual files.
1639 /proc/<pid>/coredump_filter allows you to customize which memory segments
1640 will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1641 of memory types. If a bit of the bitmask is set, memory segments of the
1642 corresponding memory type are dumped, otherwise they are not dumped.
1644 The following 9 memory types are supported:
1645 - (bit 0) anonymous private memory
1646 - (bit 1) anonymous shared memory
1647 - (bit 2) file-backed private memory
1648 - (bit 3) file-backed shared memory
1649 - (bit 4) ELF header pages in file-backed private memory areas (it is
1650 effective only if the bit 2 is cleared)
1651 - (bit 5) hugetlb private memory
1652 - (bit 6) hugetlb shared memory
1653 - (bit 7) DAX private memory
1654 - (bit 8) DAX shared memory
1656 Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1657 are always dumped regardless of the bitmask status.
1659 Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1660 only affected by bit 5-6, and DAX is only affected by bits 7-8.
1662 The default value of coredump_filter is 0x33; this means all anonymous memory
1663 segments, ELF header pages and hugetlb private memory are dumped.
1665 If you don't want to dump all shared memory segments attached to pid 1234,
1666 write 0x31 to the process's proc file.
1668 $ echo 0x31 > /proc/1234/coredump_filter
1670 When a new process is created, the process inherits the bitmask status from its
1671 parent. It is useful to set up coredump_filter before the program runs.
1674 $ echo 0x7 > /proc/self/coredump_filter
1677 3.5 /proc/<pid>/mountinfo - Information about mounts
1678 --------------------------------------------------------
1680 This file contains lines of the form:
1682 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1683 (1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11)
1685 (1) mount ID: unique identifier of the mount (may be reused after umount)
1686 (2) parent ID: ID of parent (or of self for the top of the mount tree)
1687 (3) major:minor: value of st_dev for files on filesystem
1688 (4) root: root of the mount within the filesystem
1689 (5) mount point: mount point relative to the process's root
1690 (6) mount options: per mount options
1691 (7) optional fields: zero or more fields of the form "tag[:value]"
1692 (8) separator: marks the end of the optional fields
1693 (9) filesystem type: name of filesystem of the form "type[.subtype]"
1694 (10) mount source: filesystem specific information or "none"
1695 (11) super options: per super block options
1697 Parsers should ignore all unrecognised optional fields. Currently the
1698 possible optional fields are:
1700 shared:X mount is shared in peer group X
1701 master:X mount is slave to peer group X
1702 propagate_from:X mount is slave and receives propagation from peer group X (*)
1703 unbindable mount is unbindable
1705 (*) X is the closest dominant peer group under the process's root. If
1706 X is the immediate master of the mount, or if there's no dominant peer
1707 group under the same root, then only the "master:X" field is present
1708 and not the "propagate_from:X" field.
1710 For more information on mount propagation see:
1712 Documentation/filesystems/sharedsubtree.txt
1715 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
1716 --------------------------------------------------------
1717 These files provide a method to access a tasks comm value. It also allows for
1718 a task to set its own or one of its thread siblings comm value. The comm value
1719 is limited in size compared to the cmdline value, so writing anything longer
1720 then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1724 3.7 /proc/<pid>/task/<tid>/children - Information about task children
1725 -------------------------------------------------------------------------
1726 This file provides a fast way to retrieve first level children pids
1727 of a task pointed by <pid>/<tid> pair. The format is a space separated
1730 Note the "first level" here -- if a child has own children they will
1731 not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
1732 to obtain the descendants.
1734 Since this interface is intended to be fast and cheap it doesn't
1735 guarantee to provide precise results and some children might be
1736 skipped, especially if they've exited right after we printed their
1737 pids, so one need to either stop or freeze processes being inspected
1738 if precise results are needed.
1741 3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file
1742 ---------------------------------------------------------------
1743 This file provides information associated with an opened file. The regular
1744 files have at least three fields -- 'pos', 'flags' and mnt_id. The 'pos'
1745 represents the current offset of the opened file in decimal form [see lseek(2)
1746 for details], 'flags' denotes the octal O_xxx mask the file has been
1747 created with [see open(2) for details] and 'mnt_id' represents mount ID of
1748 the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo
1757 All locks associated with a file descriptor are shown in its fdinfo too.
1759 lock: 1: FLOCK ADVISORY WRITE 359 00:13:11691 0 EOF
1761 The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1762 pair provide additional information particular to the objects they represent.
1771 where 'eventfd-count' is hex value of a counter.
1778 sigmask: 0000000000000200
1780 where 'sigmask' is hex value of the signal mask associated
1788 tfd: 5 events: 1d data: ffffffffffffffff pos:0 ino:61af sdev:7
1790 where 'tfd' is a target file descriptor number in decimal form,
1791 'events' is events mask being watched and the 'data' is data
1792 associated with a target [see epoll(7) for more details].
1794 The 'pos' is current offset of the target file in decimal form
1795 [see lseek(2)], 'ino' and 'sdev' are inode and device numbers
1796 where target file resides, all in hex format.
1800 For inotify files the format is the following
1804 inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1806 where 'wd' is a watch descriptor in decimal form, ie a target file
1807 descriptor number, 'ino' and 'sdev' are inode and device where the
1808 target file resides and the 'mask' is the mask of events, all in hex
1809 form [see inotify(7) for more details].
1811 If the kernel was built with exportfs support, the path to the target
1812 file is encoded as a file handle. The file handle is provided by three
1813 fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1816 If the kernel is built without exportfs support the file handle won't be
1819 If there is no inotify mark attached yet the 'inotify' line will be omitted.
1821 For fanotify files the format is
1826 fanotify flags:10 event-flags:0
1827 fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
1828 fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
1830 where fanotify 'flags' and 'event-flags' are values used in fanotify_init
1831 call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
1832 flags associated with mark which are tracked separately from events
1833 mask. 'ino', 'sdev' are target inode and device, 'mask' is the events
1834 mask and 'ignored_mask' is the mask of events which are to be ignored.
1835 All in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
1836 does provide information about flags and mask used in fanotify_mark
1837 call [see fsnotify manpage for details].
1839 While the first three lines are mandatory and always printed, the rest is
1840 optional and may be omitted if no marks created yet.
1851 it_value: (0, 49406829)
1854 where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
1855 that have occurred [see timerfd_create(2) for details]. 'settime flags' are
1856 flags in octal form been used to setup the timer [see timerfd_settime(2) for
1857 details]. 'it_value' is remaining time until the timer exiration.
1858 'it_interval' is the interval for the timer. Note the timer might be set up
1859 with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
1860 still exhibits timer's remaining time.
1862 3.9 /proc/<pid>/map_files - Information about memory mapped files
1863 ---------------------------------------------------------------------
1864 This directory contains symbolic links which represent memory mapped files
1865 the process is maintaining. Example output:
1867 | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
1868 | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
1869 | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
1871 | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
1872 | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
1874 The name of a link represents the virtual memory bounds of a mapping, i.e.
1875 vm_area_struct::vm_start-vm_area_struct::vm_end.
1877 The main purpose of the map_files is to retrieve a set of memory mapped
1878 files in a fast way instead of parsing /proc/<pid>/maps or
1879 /proc/<pid>/smaps, both of which contain many more records. At the same
1880 time one can open(2) mappings from the listings of two processes and
1881 comparing their inode numbers to figure out which anonymous memory areas
1882 are actually shared.
1884 3.10 /proc/<pid>/timerslack_ns - Task timerslack value
1885 ---------------------------------------------------------
1886 This file provides the value of the task's timerslack value in nanoseconds.
1887 This value specifies a amount of time that normal timers may be deferred
1888 in order to coalesce timers and avoid unnecessary wakeups.
1890 This allows a task's interactivity vs power consumption trade off to be
1893 Writing 0 to the file will set the tasks timerslack to the default value.
1895 Valid values are from 0 - ULLONG_MAX
1897 An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
1898 permissions on the task specified to change its timerslack_ns value.
1900 3.11 /proc/<pid>/patch_state - Livepatch patch operation state
1901 -----------------------------------------------------------------
1902 When CONFIG_LIVEPATCH is enabled, this file displays the value of the
1903 patch state for the task.
1905 A value of '-1' indicates that no patch is in transition.
1907 A value of '0' indicates that a patch is in transition and the task is
1908 unpatched. If the patch is being enabled, then the task hasn't been
1909 patched yet. If the patch is being disabled, then the task has already
1912 A value of '1' indicates that a patch is in transition and the task is
1913 patched. If the patch is being enabled, then the task has already been
1914 patched. If the patch is being disabled, then the task hasn't been
1918 ------------------------------------------------------------------------------
1920 ------------------------------------------------------------------------------
1923 ---------------------
1925 The following mount options are supported:
1927 hidepid= Set /proc/<pid>/ access mode.
1928 gid= Set the group authorized to learn processes information.
1930 hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
1933 hidepid=1 means users may not access any /proc/<pid>/ directories but their
1934 own. Sensitive files like cmdline, sched*, status are now protected against
1935 other users. This makes it impossible to learn whether any user runs
1936 specific program (given the program doesn't reveal itself by its behaviour).
1937 As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
1938 poorly written programs passing sensitive information via program arguments are
1939 now protected against local eavesdroppers.
1941 hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
1942 users. It doesn't mean that it hides a fact whether a process with a specific
1943 pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
1944 but it hides process' uid and gid, which may be learned by stat()'ing
1945 /proc/<pid>/ otherwise. It greatly complicates an intruder's task of gathering
1946 information about running processes, whether some daemon runs with elevated
1947 privileges, whether other user runs some sensitive program, whether other users
1948 run any program at all, etc.
1950 gid= defines a group authorized to learn processes information otherwise
1951 prohibited by hidepid=. If you use some daemon like identd which needs to learn
1952 information about processes information, just add identd to this group.
git.samba.org / sfrench / cifs-2.6.git / blob